Selecting A Seal 2016-12-29T09:16:30+00:00

Selecting A Seal

It must first be decided whether the sealing element is to be synthetic rubber or leather. Many factors determine this, for example, media to be sealed, temperature, shaft speeds, surface finish, etc., and all must be carefully considered.
Generally leather elements would be more used for more arduous applications having moderate shaft speeds, pressures and temperatures of -30°C ti +90°C (-13°F to +194°F). Synthetic rubber (nitrile®) seals will accommodate temperatures of -25°C to +120°C (-13°F to +248°F) and, by the very nature of their design, greater surface speeds and pressures.

With sophisticated rubber we are able to increase the temperature range quite considerably, for example, silicone rubber -60°C to +200°C (-76°F to +392°F) and fluoroelastomer (FPM) rubber -15°C to +250°C (+5°F to +482°F). It must be stressed however, that these are the maximum limits for the material used and must be grouped together with the other application details before final selection is made. EPM would be pleased to offer advice on the correct materials, should the need arise.

Click here to view illustrations of our different type seal lips.

Also available are the following variations of seal design, which are not illustrated on this site but identified by suffix letters:
D3S, D3RS, D4S, D4RS = Semi-Dual seals having the wiping lip straight cut as opposed to angle trimmed.
H = High pressure piercing
B = Brass casings & washers
SS = Stainless steel casings & washers
T3 = Triple seals with lips in tandem
T4 = Triple seal with one sealing lip opposed
SL = Soft leather (not waxed)


Seals should be stored at room temperature in a clean, dry atmosphere. They should be kept in the protective paper in which they are received until they are ready for assembly. 

If the nature moisture found in leather dries out during storage and the element becomes hard, you will restore flexibility by soaking them in warm oil at 25/30°C (77/86°F) for not less than 15 minutes. Before commencing this operation, however, the source of heat must be removed. Do not throw seals into bins, stack them in irregular piles or tie them up with string or wire. Treat them for what they are – an important engineering component. 

Check that the housing, shaft and seal are clean, as foreign matter, however small, can have an adverse effect on the sealing performance. 

Having satisfied yourself in this respect, apply a thin film of general purpose grease to the sealing element to assist assembly. This is imperative in case of synthetic rubber. Dual/Triple seals need to have the cavity between the lips pre-packed with grease, as there is a danger that one of the lips may not receive adequate lubrication under working conditions. By applying this grease the life of this type seal will be greatly increased.housing_dia 

The outside diameter of internal seals will have a predetermined interference allowing them to be press fitted into their housings. It is imperative that they are assembled square by exerting a firm uniform pressure. The ideal situation is by means of an arbor tool which should be 0.005″ to 0.015″ (0.125 to 0.38mm) less than the outside diameter of the seal. If you are unable to use an arbor press then make a fitting tool. DO NOT under any circumstances fit seals with a drift and hammer as irregular blows exerted by this method may loosen the metal parts which will release the clamping of the internal components.


Care must always be exercised when assembling seals on to the shaft to avoid damage to the sealing edge. If a lead-in chamfer/radius has not been provided or if the seal has to pass over a key-way, then it is necessary to provide a fitting sleeve as illustrated. Noncompliance with these instructions can lead to either the lips being turned back or cut, particularly in the case of rubber. There is also the possibility of the spring becoming dislodged, which, after the element has been returned to its normal position, will mean there is a danger of it making contact with the shaft, with the resultant disastrous effects. The application of a liberal smear of grease on the internal side of the element will greatly assist the seals assembly. 

Normal practice is for the wiping edge of the seal to be facing the media to be sealed, and it is in this direction that it will hold against pressure. If, however, pressure conditions do not exist then the seal can be assembled to face the other way around. 

This is particularly advantageous in grease lubricated applications as this will allow the discharge of any contaminated lubricant from the sealing area when the grease gun is applied. This will then ensure clean lubrication of the seal lip and reduce unnecessary wear from abrasive elements. 

During maintenance/overhauling of equipment we strongly recommend that a new seal be fitted. Under no circumstances should the old seal be removed and then replaced in the same housing, the interference fit cannot be repeated. 

If there is no alternative but to use the old seal then do take extra care:
1. Make sure that the sealing edge is not damaged in any way.
2. Check the shaft for wear/marks. Make sure that the area on which the seal is to run is in good condition.
3. Apply a liberal amount of clean grease or mineral oil to the sealing edge before offering the shaft back through.

Contact Us

EPM, Inc.
112 W Burke St.
Stockbridge, GA 30281

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Call Free in the US: 800.659.5050
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